Temperature of an engine internal component may vary with engine operating conditions. One engine component temperature that varies with engine operating conditions is engine piston temperature. For example, piston temperature may vary with engine speed, load, combustion timing, fuel type, fuel injection timing, and other conditions. At higher engine loads, end gases in an engine cylinder may combust after an initial spark in the cylinder, but before being ignited by a flame produced by the spark. The end gases may begin to combust as a result of being exposed to higher piston temperatures. Consequently, the engine may knock and engine component degradation may result. One way to reduce piston temperature and the possibility of knock is to spray engine oil on the bottom sides of pistons. The oil conducts heat away from the piston, thereby cooling the piston. The heated oil returns to the oil pan via gravity where it may be cooled. However, engine energy is used to spray oil on the pistons and engine fuel economy may decrease when engine oil is sprayed on pistons.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: operating a piston cooling jet in response to an engine torque difference between operating at a borderline spark while operating the piston cooling jet at an engine speed and load, and operating at a borderline spark while not operating the piston cooling jet at the engine speed and load.
By selectively operating a piston cooling jet in response to an engine torque difference between operating at a borderline spark while operating the piston cooling jet at an engine speed and load, and operating at a borderline spark while not operating the piston cooling jet at the engine speed and load, it may be possible to conserve fuel by not operating the piston cooling jet when operating the piston cooling jet provides little benefit. On the other hand, the piston cooling jet may be operated when operating the piston cooling jet provides more useful benefit.
The present description may provide several advantages. For example, the approach may improve engine fuel economy. Additionally, the approach may provide piston cooling during conditions where it provides a significant benefit. Further, the approach may be useful for engine systems that do or do not include individual control of piston cooling jets.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.